1. Field of the Invention
The present invention relates to semiconductor devices, and more particularly to a semiconductor device having a hydrogen trapping function by insertion of a silicon oxynitride film.
2. Description of the Background Art
Multilevel interconnection configuration has increasingly been employed to achieve higher integration and higher performance of devices. To fabricate a semiconductor device having multilevel interconnections, for example, a lower-layer aluminum interconnection is formed firstly, and a silicon oxynitride film serving as an interlayer insulating film is formed on the lower-layer aluminum interconnection by CVD (Chemical Vapor Deposition) or SOG (Spin On Glass), and then an upper-layer aluminum interconnection is formed on the silicon oxynitride film.
Such multilevel interconnection configuration leads to an increase in complexity as well as a higher aspect ratio of the uneven surface portion of the element, which may cause a break of wire. Thus, for the purposes of increasing the yield of the interconnections and improving reliability, planarization and smoothing are important. Currently, a TEOS (Tetra Ethoxy Silane)/O3 oxide film, a SOG film or the like has been used for such planarization and smoothing.
The silicon oxide film formed by CVD or SOG, however, contains a large amount of water (H2O or OH), which causes degradation in reliability of the device, particularly, degradation of hot-carrier resistance of a MOSFET (Metal-Oxide Semiconductor Field-Effect Transistor). To suppress such degradation due to the water from the TEOS/O3 film, it has been reported that an ECR (Electron Cyclotron Resonance)-SiO2 film may be deposited under the TEOS/O3 film, in which case a great number of dangling bonds present in the ECR-SiO2 film can capture water from the TEOS/O3 oxide film to prevent penetration of the water to the device (see N. Shimoyama et al., “Enhanced Hot-Carrier Degradation due to Water in TEOS/O3 Oxide and a New Method of Water Blocking using ECR-SiO2 Film”, SDM 92-33, pp. 51-56).
Further, there is another way of addressing this problem of water by depositing an oxide film on a first interconnection by plasma CVD, to block water desorbing from an insulating film provided in its upper layer. It has been reported that a SiO2 film formed by plasma CVD using SiH4 and N2O gases under a low pressure of 1.5 Torr, and a TEOS film formed by plasma CVD by lowering the flow rate of TEOS/O3, can block water and suppress MOSFET hot-carrier degradation (see Kimiaki Shimokawa et al., “Water Desorption Control of Interlayer Dielectrics to Reduce MOSFET Hot Carrier Degradation”, IEICE TRANS. ELECTRON., VOL. E77-C, NO. 3, March 1994, pp. 473-479).
Meanwhile, it is known that a Si-rich and N-rich plasma CVD film can block water from an interlayer insulating film such as a SOG film. This film can readily be formed with SiH4 and N2O gases by adding N2 gas under a low pressure, and has a function of absorbing water and releasing hydrogen (see Peter Lee et al., “MOISTURE TRAPPING AND PINHOLE SUPPRESSION BY THE USE OF HIGH REFRACTIVE INDEX PECVD SIO2 THIN FILM”, VMIC Conference, Jun. 7-8, 1994, ISMIC-103/94/0299, pp. 299-301).
Further, it has been reported that, in a semiconductor device having an insulating film formed by CVD using a source gas having Si—H bonds, moisture resistance is improved by setting the amount of the Si—H bonds in the insulating film to 0.6×1021 cm−3 or less and by setting N concentration to 3×1021 cm−3 or more, and thus, after completion of the semiconductor device, water is prevented from reaching a metal interconnection such as aluminum, resulting in improved reliability of the semiconductor device. The insulating film is formed on the interconnection, or is used as a passivation film (see Japanese Patent Laying-Open No. 09-289209).
Still further, a semiconductor device having a Si-rich oxide film, a Si oxide film, a SOG film and an oxide film formed sequentially on a lower-layer metal interconnection is known. The Si-rich oxide film, serving as an interlayer insulating film, is formed on the metal interconnection, or is used as a passivation film. It is reported that this semiconductor device ensures hot carrier reliability and good performance characteristic of the semiconductor element (see Japanese Patent Laying-Open No. 09-129625).